In lithography technologies to form an interconnection pattern or the like, in association with trends towards extreme fine pattern designing, it is difficult to form a pattern using an optical lithography technology as a conventional general-purpose technology. To realize finer pattern designing, exposure technologies using charged-particle beams such as electron beams or ion beams, and short-wavelength beams from an X-ray source are being considered with optimism. Among them, in an electron-beam delineation technology, an initial point-beam delineation and a variable-shape delineation method for changing the size or shape of a rectangular beam to delineating a pattern have been proposed. In addition a cell projection delineation method for delineating a part of a pattern partially together through a mask and repeating such a processing has been proposed from the viewpoint of an improvement of the pattern accuracy and a reduction in delineation time, and the technology has been developed. Subsequent to the cell projection delineation method, S. D. Berger et al. proposed a new electron-beam projection system (SCALPEL system) about eight years ago. After that, a similar delineation system (PREVAIL system) and various proposals regarding a transfer mask (reticle) structure to be applied to those delineation systems, and a method for manufacturing the mask, have been made.
For example, Japanese Patent No. 2829942 (Japanese Unexamined Patent Application Publication No. 7-201726) relates to the PREVAIL system invented by H. C. Pfeiffer et al. In brief a stencil mask is prepared in which an opening (aperture) pattern with a predetermined size is formed in a predetermined arrangement in each small field. Charged-particle beams are irradiated to the small fields. The opening pattern is reduced and transferred to an exposed substrate, on which a photosensitive material is formed, using the beams shaped by the opening pattern through an optical system. The predetermined patterns divided (split) and formed on the mask are connected to each other on the exposed substrate to form a device pattern. As a transfer mask proposed for such a system, a stencil type mask in which a pattern portion comprises an opening that is not shielded completely is used as a main structure (Japanese Unexamined Patent Application Publication No. 10-261584, Japanese Unexamined Patent Application Publication No. 10-260523, or the like). For the stencil type mask, the backside surface of a pattern field is split and reinforced by a strut (bridge) structure, thereby improving a reduction in distortion of the pattern field. Consequently, pattern position accuracy is improved.
As a mask structure for the SCALPEL system, a scattering mask (reticle) is proposed other than the stencil mask. Those are specifically described in, for example, a cited document (by S. D. Berger & J. M. Gibson, APPL. PHYS. LETTERS 57 (2) (1990) 153), Japanese Unexamined Patent Application Publication No. 10-261584, and Japanese Unexamined Patent Application Publication No. 10-321495. In the above references, for the mask structure, a heavy-metal film is formed on a membrane (self-supporting thin film) made of SiN or the like and a desired pattern is formed into the heavy-metal film. According to a method using the mask structure, electron beams are irradiated to both the films. The electron scattering degrees of the films differs depending on the presence or absence of an electron-beam scatterer. Exploiting the difference of the scattering degrees, beam contrast on a wafer is obtained, thereby reducing and transferring the pattern.
According to those exposure systems, high-resolution properties serving as features of the charged-particle beams are obtained and a pattern finer than 0.1 μm can be formed. Compared with the cell projection method, due to sharp enlargement of a shot size (for example, the maximum shot size on the exposed substrate is increased from 5 μm to 250 μm), throughput in production of a device is improved (for example, in case of an 8-inch substrate having the minimum line width of 0.08 μm, throughput of 30 wafers/hour or higher). The system is capable of manufacturing a general-purpose device and is of much practical use.
As mentioned above, in the electron-beam projection exposure (EPL: PREVAIL, SCALPEL), two kinds of mask structures, namely, the stencil type and the membrane type are proposed. The stencil mask is fabricated using an SOI wafer by shaping processing such as dry etching. Since mask magnification is set to low magnification, for example, 4 times, the mask pattern is extremely fine. For the thickness, 2 μm is standard from the viewpoint of workability and heat conductivity. The stencil type conventionally has a problem regarding the drop of a ring pattern called “a doughnut problem.” Consequently, a complementary mask method for performing pattern split has been proposed. However, in association with finer pattern designing, the mechanical strength (intensity) is may be adversely affected, depending on the pattern formed in the transfer field. It is considered that complementary division in a wide area is needed.
As related arts regarding the complementary division of the pattern, for example, Japanese Unexamined Patent Application Publication No. 11-26372 is mentioned. This publication discloses that a cantilever pattern low-supporting pattern: pattern in which one end is connected to a mask material) needs complementary division. This publication also discloses that a pattern in which both ends are supported has no problem of mechanical strength.
However, especially in a cantilever (leaf) portion or a line and space pattern (an L&S bridge portion), there is concern regarding mask workability due to low mechanical strength and breakage caused by stress concentration. The present inventor has studied the relation between the pattern size and the intensity of the cantilever pattern and the relation with the intensity of the both-end-supported pattern, thereby accomplishing the present invention.